The present invention relates to electrical and electronic components. More particularly, it is concerned with electrically conductive bearing retainers.
Bearing retainers are used to separate and position the bearings that support motor driven joints in apparatus such as turret systems for airborne, ground and sea based platforms. These turret assemblies may hang on/under a variety of operational platforms, including but not limited to, helicopters, unmanned aerial vehicles, fixed wing aircraft, ground and marine vehicles and the like.
The turret assemblies may employ gimbals consisting of two rotating components (azimuth and elevation) to accurately distinguish, track, and eliminate targets. The dynamic azimuth and elevation interfaces are bearing supported, motor driven joints that contain dynamic environmental seals. These dynamic interfaces may have very high resistances because ball bearing contact is minimal between the inner and outer races of the bearing. The motors are often powered with high frequency voltages that can generate extremely strong electromagnetic interference radiation (EMI) emissions. The lack of conductivity between these dynamic interfaces allows EMI emissions to radiate from the system instead of grounding to the chassis or helicopter.
EMI is electromagnetic radiation emitted by electrical circuits carrying rapidly changing signals, as a by-product of their normal operation. EMI causes unwanted signals (interference or noise) to be induced in other circuits. These interferences can interrupt, obstruct or otherwise degrade or limit the effective performance of the other circuits. EMI can be induced intentionally, as in some forms of external electronic warfare or unintentionally as a result of spurious emissions and the like. EMI emissions can cause severe operational platform complications such as flight, guidance, and weapon control interference. In addition, any system having large EMI emissions can be detected easily and tracked by enemy forces.
Electrical resistance “R”, measured in ohms Ω, is a measure of the degree to which an object opposes the passage of an electric current. Materials with high resistance values are considered to be poor conductors of electricity, while materials having low resistance values are considered to be good conductors. In previous turret systems, electrical resistances of between about 1Ω and about 4Ω were considered to be acceptable. Under current standards, the acceptable electrical resistance values have decreased by about 1600 fold and must be below about 2.5 milliohms to meet customer/program requirements.
Complex turret systems may contain numerous electrical components that can generate EMI emissions. As the sophistication of these turret assemblies continues to develop with advances in technology and war-fighting capabilities, EMI issues are continuously on the rise. A Faraday cage may be employed to suppress both internally generated and externally induced EMI. A Faraday cage, often simply referred to as a shield, is an enclosure formed of a conductive material and designed to exclude electromagnetic fields in an application of Gauss' law. Gauss' law describes the distribution of electrical charge on an electrically conductive form, such as a sphere, plane, torus, or gimbal etc. Since like charges repel each other, the charge will ‘migrate’ to the surface of the conducting form. A Faraday cage volume can be created by adding a network of conductive contacts between rotating gimbal interfaces. As internally generated EMI approaches the inside wall of the gimbal Faraday cage volume, charge will be absorbed and transferred back to the chassis ground. This absorption eliminates EMI emissions which would otherwise exit the gimbal. The Faraday cage also shields the interior from the entry of external EMI.
Given the inherent rotational characteristics of gimbals, it can be difficult and expensive to complete a Faraday cage volume across a gimbal bearing. The ball bearings that enable gimbals to rotate are generally made from steel having low electrical conductivity. In addition, lubricated single point bearing contacts between the inner and outer bearing races have extremely high electrical resistance values, indicating that they are poor conductors of electricity.
The general rotational dynamics of these sophisticated turrets, their increasingly complicated electronics, stronger torque motors, and varying materials all serve to increase the difficulties associated with containing and eliminating EMI. At the same time, continued development of enemy countermeasures necessitates further suppression of radiated EMI emissions.